Medical couch apparatuses have a couch body, a top having a subject mounted thereon, and a driving unit. The couch body includes a linear guide for guiding the top in the rostrocaudal direction. In addition, the couch body includes a pinion. The top includes a rack which slides so as to mesh with the pinion. The driving unit transfers the top in the rostrocaudal direction by rotating the pinion using a motor as a power source (for example, Patent Document 1). Further, the rostrocaudal direction is sometimes referred to as the Z direction. In addition, one direction of the rostrocaudal direction is sometimes referred to as the Z1 direction, while the other rostrocaudal direction is sometimes referred to as the Z2 direction.
A power sequence circuit is provided to control the power source supplied to the motor, or the like. The power sequence circuit includes a relay. Further, an operation switch is provided for preventing the power source from being supplied to the motor. The operation switch is sometimes referred to as an emergency stop switch.
If the operation switch is operated during transfer of the top in the rostrocaudal direction by the motor, the power source supplied to be provided to the motor is interrupted through the operation of the relay in the power sequence circuit, and the top is braked to stop by the retention of the motor.
Hereinafter, the relation between the transfer velocity (constant velocity) at the time that the top is transferring and the distance until the top is stopped after operating the operation switch will be described with reference to FIG. 11.
FIG. 11 is a view showing the relation between the transfer velocity and the stop distance of the top as a comparative example.
The transfer distance of the top until the top is stopped after operating the operation switch during transfer of the top is sometimes referred to as a stop distance or an emergency stop distance, the transfer distance of the top during an idle running time until the top is braked after operating the operation switch is sometimes referred to as an idle running distance, and the transfer distance of the top during the braking time until the top is stopped after braking is sometimes referred to as a braking distance. The idle running time is generated due to the response delay time until the power source supplied to the motor is interrupted after operating the operation switch, as the relay of the power sequence circuit undergoes an operation delay. The idle running distance is generated as the motor is rotated and the top is transferred during the response delay time.
FIG. 11 depicts the idle running time [sec] as “t1” and the braking time [sec] as “t2.” In addition, FIG. 11 illustrates a velocity diagram shown by a bold line with the transfer velocity (constant velocity) [mm/s] defined as “V” when the top is transferred. Further, the stop distance [mm] at the velocity V is represented as “d,” the idle running distance [mm] is represented as “d1,” and the braking distance [mm] is represented as “d2.”
Thereby, the d1 and d2 are represented respectively by the following formulas.d1=V·t1  (2)d2=V·t2/2  (3)
The stop distance d is obtained by adding the idle running distance d1 and the control distance d2, and it makes the d to be represented by the following formula using the formulas (2), (3).d=V·t1+V·t2/2  (4)
Recently, speeding up for transferring the top at high velocities has been promoted. FIG. 11 illustrates a velocity diagram shown by a bold dashed line when the top is transferred at high velocities. FIG. 11 depicts the velocity when the top is transferred at high velocities as “Vh,” the stop distance [mm] as “dh,” the idle running distance [mm] as “d3,” and the braking distance [mm] as “d4.” Further, it is assumed that the force to brake the top (braking force) is the same at the velocity V and at the high velocity Vh. Accordingly, the control time at the high velocity Vh becomes twice the braking time t2 at the velocity V (2t2.)
Thereby, the d3, d4, and dh are respectively represented by the following formulas.d3=Vh·t1  (5)d4=Vh·2t2  (6)dh=Vh·t1+Vh·2t2  (7)
Here, assuming that the high velocity Vh is twice the velocity V, the Vh and dh are represented by the following formulas.Vh=2V  (8)dh=2V·t1+2V·t2  (9)
The following formula is established from the formula (9).dh=2d+V·t2  (10)
It is known from the formula (10) that the stop distance becomes double or more if the top is transferred at twice the velocity.
Generally, the higher the transferring velocity of the top becomes, the longer the stop distance becomes. Further, it is sometimes referred to as an overrun when the top exceeds a specific distance, while the amount by which the top exceeds the specific distance is sometimes referred to as the overrun amount.
Even if the top is transferred at high velocities, in terms of ensuring safety, it is necessary to stop the top within the specific distance.
However, the higher the transferring velocity of the top becomes, the longer the stop distance becomes in conventional medical couch apparatuses, therefore, it has been necessary to set a limit value to the highest velocity of the top in order to stop the top within the specific distance. Setting no limitation value to the highest velocity has been problematic in that the overrun easily occurs.